YAML :: load引发未定义的类/模块错误

Question

我正在我的rails应用程序中实现类似于纸张跟踪的功能.为了做到这一点,我在YAML中序列化对象.我有item_at_version方法,基本上做YAML::load(cached_object)- 这很好用,但是,我不知道为什么,有时它会返回undefined class/module _class name_.它适用于像Event,Conversation,Note等模型,但没有任何理由,它似乎为像Dataset,Comment,Student这样的模型抛出了这个错误(我试图找到任何模式,没有任何运气) .

我使用rails 3.2.8,ruby 1.9.3p327,psych作为YAML Engine(Psych :: Version返回1.3.4).

PS.当我在该文件的顶部添加require'model_name'时,它就像一个魅力.

任何想法我应该改变/添加什么来使这个工作？

编辑:我可以分享的代码不多:

def item_at_version
  YAML::load(cached_object)
end

但也许回溯会很有趣:

~/.rvm/rubies/ruby-1.9.3-p327/lib/ruby/1.9.1/psych/visitors/to_ruby.rb:312:in `path2class'
~/.rvm/rubies/ruby-1.9.3-p327/lib/ruby/1.9.1/psych/visitors/to_ruby.rb:312:in `resolve_class'
~/.rvm/rubies/ruby-1.9.3-p327/lib/ruby/1.9.1/psych/visitors/to_ruby.rb:219:in `visit_Psych_Nodes_Mapping'
~/.rvm/rubies/ruby-1.9.3-p327/lib/ruby/1.9.1/psych/visitors/visitor.rb:15:in `visit'
~/.rvm/rubies/ruby-1.9.3-p327/lib/ruby/1.9.1/psych/visitors/visitor.rb:5:in `accept'
~/.rvm/rubies/ruby-1.9.3-p327/lib/ruby/1.9.1/psych/visitors/to_ruby.rb:20:in `accept'
~/.rvm/rubies/ruby-1.9.3-p327/lib/ruby/1.9.1/psych/visitors/to_ruby.rb:238:in `visit_Psych_Nodes_Document'
~/.rvm/rubies/ruby-1.9.3-p327/lib/ruby/1.9.1/psych/visitors/visitor.rb:15:in `visit'
~/.rvm/rubies/ruby-1.9.3-p327/lib/ruby/1.9.1/psych/visitors/visitor.rb:5:in `accept'
~/.rvm/rubies/ruby-1.9.3-p327/lib/ruby/1.9.1/psych/visitors/to_ruby.rb:20:in `accept'
~/.rvm/rubies/ruby-1.9.3-p327/lib/ruby/1.9.1/psych/nodes/node.rb:35:in `to_ruby'
~/.rvm/rubies/ruby-1.9.3-p327/lib/ruby/1.9.1/psych.rb:128:in `load'
app/models/history_version.rb:7:in `item_at_version'
app/controllers/history_controller.rb:8:in `show'
actionpack (3.2.8) lib/action_controller/metal/implicit_render.rb:4:in `send_action'
actionpack (3.2.8) lib/abstract_controller/base.rb:167:in `process_action'
actionpack (3.2.8) lib/action_controller/metal/rendering.rb:10:in `process_action'
actionpack (3.2.8) lib/abstract_controller/callbacks.rb:18:in `block in process_action'
activesupport (3.2.8) lib/active_support/callbacks.rb:502:in `_run__1697733322876708236__process_action__1122943786273335015__callbacks'
activesupport (3.2.8) lib/active_support/callbacks.rb:405:in `__run_callback'
activesupport (3.2.8) lib/active_support/callbacks.rb:385:in `_run_process_action_callbacks'
activesupport (3.2.8) lib/active_support/callbacks.rb:81:in `run_callbacks'
actionpack (3.2.8) lib/abstract_controller/callbacks.rb:17:in `process_action'
actionpack (3.2.8) lib/action_controller/metal/rescue.rb:29:in `process_action'
actionpack (3.2.8) lib/action_controller/metal/instrumentation.rb:30:in `block in process_action'
activesupport (3.2.8) lib/active_support/notifications.rb:123:in `block in instrument'
activesupport (3.2.8) lib/active_support/notifications/instrumenter.rb:20:in `instrument'
activesupport (3.2.8) lib/active_support/notifications.rb:123:in `instrument'
actionpack (3.2.8) lib/action_controller/metal/instrumentation.rb:29:in `process_action'
actionpack (3.2.8) lib/action_controller/metal/params_wrapper.rb:207:in `process_action'
activerecord (3.2.8) lib/active_record/railties/controller_runtime.rb:18:in `process_action'
actionpack (3.2.8) lib/abstract_controller/base.rb:121:in `process'
actionpack (3.2.8) lib/abstract_controller/rendering.rb:45:in `process'
actionpack (3.2.8) lib/action_controller/metal.rb:203:in `dispatch'
actionpack (3.2.8) lib/action_controller/metal/rack_delegation.rb:14:in `dispatch'
actionpack (3.2.8) lib/action_controller/metal.rb:246:in `block in action'
actionpack (3.2.8) lib/action_dispatch/routing/route_set.rb:73:in `call'
actionpack (3.2.8) lib/action_dispatch/routing/route_set.rb:73:in `dispatch'
actionpack (3.2.8) lib/action_dispatch/routing/route_set.rb:36:in `call'
journey (1.0.4) lib/journey/router.rb:68:in `block in call'
journey (1.0.4) lib/journey/router.rb:56:in `each'
journey (1.0.4) lib/journey/router.rb:56:in `call'
actionpack (3.2.8) lib/action_dispatch/routing/route_set.rb:600:in `call'
actionpack (3.2.8) lib/action_dispatch/middleware/best_standards_support.rb:17:in `call'
rack (1.4.1) lib/rack/etag.rb:23:in `call'
rack (1.4.1) lib/rack/conditionalget.rb:25:in `call'
actionpack (3.2.8) lib/action_dispatch/middleware/head.rb:14:in `call'
actionpack (3.2.8) lib/action_dispatch/middleware/params_parser.rb:21:in `call'
actionpack (3.2.8) lib/action_dispatch/middleware/flash.rb:242:in `call'
rack (1.4.1) lib/rack/session/abstract/id.rb:205:in `context'
rack (1.4.1) lib/rack/session/abstract/id.rb:200:in `call'
actionpack (3.2.8) lib/action_dispatch/middleware/cookies.rb:339:in `call'
activerecord (3.2.8) lib/active_record/query_cache.rb:64:in `call'
activerecord (3.2.8) lib/active_record/connection_adapters/abstract/connection_pool.rb:473:in `call'
actionpack (3.2.8) lib/action_dispatch/middleware/callbacks.rb:28:in `block in call'
activesupport (3.2.8) lib/active_support/callbacks.rb:405:in `_run__2589517259026276185__call__1369641113040304056__callbacks'
activesupport (3.2.8) lib/active_support/callbacks.rb:405:in `__run_callback'
activesupport (3.2.8) lib/active_support/callbacks.rb:385:in `_run_call_callbacks'
activesupport (3.2.8) lib/active_support/callbacks.rb:81:in `run_callbacks'
actionpack (3.2.8) lib/action_dispatch/middleware/callbacks.rb:27:in `call'
actionpack (3.2.8) lib/action_dispatch/middleware/reloader.rb:65:in `call'
actionpack (3.2.8) lib/action_dispatch/middleware/remote_ip.rb:31:in `call'
bugsnag (1.2.5) lib/bugsnag/rack.rb:35:in `call'
actionpack (3.2.8) lib/action_dispatch/middleware/debug_exceptions.rb:16:in `call'
actionpack (3.2.8) lib/action_dispatch/middleware/show_exceptions.rb:56:in `call'
railties (3.2.8) lib/rails/rack/logger.rb:26:in `call_app'
railties (3.2.8) lib/rails/rack/logger.rb:16:in `call'
quiet_assets (1.0.1) lib/quiet_assets.rb:20:in `call_with_quiet_assets'
actionpack (3.2.8) lib/action_dispatch/middleware/request_id.rb:22:in `call'
rack (1.4.1) lib/rack/methodoverride.rb:21:in `call'
rack (1.4.1) lib/rack/runtime.rb:17:in `call'
activesupport (3.2.8) lib/active_support/cache/strategy/local_cache.rb:72:in `call'
rack (1.4.1) lib/rack/lock.rb:15:in `call'
actionpack (3.2.8) lib/action_dispatch/middleware/static.rb:62:in `call'
railties (3.2.8) lib/rails/engine.rb:479:in `call'
railties (3.2.8) lib/rails/application.rb:223:in `call'
railties (3.2.8) lib/rails/railtie/configurable.rb:30:in `method_missing'
~/Library/Application Support/Pow/Versions/0.4.0/node_modules/nack/lib/nack/server.rb:147:in `handle'
~/Library/Application Support/Pow/Versions/0.4.0/node_modules/nack/lib/nack/server.rb:99:in `rescue in block (2 levels) in start'
~/Library/Application Support/Pow/Versions/0.4.0/node_modules/nack/lib/nack/server.rb:96:in `block (2 levels) in start'
~/Library/Application Support/Pow/Versions/0.4.0/node_modules/nack/lib/nack/server.rb:86:in `each'
~/Library/Application Support/Pow/Versions/0.4.0/node_modules/nack/lib/nack/server.rb:86:in `block in start'
~/Library/Application Support/Pow/Versions/0.4.0/node_modules/nack/lib/nack/server.rb:66:in `loop'
~/Library/Application Support/Pow/Versions/0.4.0/node_modules/nack/lib/nack/server.rb:66:in `start'
~/Library/Application Support/Pow/Versions/0.4.0/node_modules/nack/lib/nack/server.rb:13:in `run'
~/Library/Application Support/Pow/Versions/0.4.0/node_modules/nack/bin/nack_worker:4:in `<main>'

Answer 1

当您使用YAML.dumpRuby中的对象序列化时,类名称将用作Yaml标记的一部分,以便在加载对象时可以使用正确的类.例如:

require 'yaml'

class Foo; end

puts YAML.dump Foo.new

产生

--- !ruby/object:Foo {}

当您YAML.load在该字符串上使用时,Psych知道要为反序列化对象实例化的类.

如果您尝试调用YAML.load指定尚未定义的类的Yaml字符串,那么您将收到错误:

require 'yaml'

# No Bar class has been defined
YAML.load '--- !ruby/object:Bar {}'

生产:

/Users/matt/.rvm/rubies/ruby-1.9.3-p327/lib/ruby/1.9.1/psych/visitors/to_ruby.rb:312:in `path2class': undefined class/module Bar (ArgumentError)
    from /Users/matt/.rvm/rubies/ruby-1.9.3-p327/lib/ruby/1.9.1/psych/visitors/to_ruby.rb:312:in `resolve_class'
...

这是因为Psych需要创建一个类的实例Bar,但没有可用的类的定义.这解释了为什么require 'whatever'在加载Yaml之前添加工作 - 现在Ruby已经加载了类的定义,因此可以创建它的实例(请注意,Ruby中的类名和文件名之间没有明确的链接,这只是惯例).

因此,解决方案是确保当您从Yaml加载任何Ruby对象时,您已经需要任何可能包含该Yaml中可能包含的任何类的定义的文件.